Apple not only released a preview of its next operating system, Mac OS X Lion, to developers today, the company is also giving it to security experts for review.

"I wanted to let you know that I've requested that you be invited to the prerelease seed of Mac OS X Lion, and you should receive an invitation soon," said a letter sent by Apple to an unknown number of security researchers. "As you have reported Mac OS X security issues in the past, I thought that you might be interested in taking a look at this. It contains several improvements in the area of security countermeasures."

Dino Dai Zovi and several other researchers tweeted about being invited to try out the prerelease version of the new Mac OS. "This looks to be a step in the direction of opening up a bit and inviting more dialogue with external researchers," Dai Zovi wrote. "I won't be able to comment on it until its release, but hooray for free access!"

I asked Charlie Miller, another expert on Mac security, if this was the first time Apple had offered to show an OS preview to security experts, and what the significance is.

"As far as I know they have never reached out to security researchers in this way. Also, we won't have to pay for it like everybody else," he wrote in an e-mail. "It's not hiring us to do pen-tests of it, but at least it's not total isolation anymore, and at least security crosses their mind now."

"I haven't downloaded it yet, but if I had, I couldn't talk about it," he added. "Damn NDAs."